Domino

The image contains 27 dominoes. A standard double-six domino set has 28 unique tiles. Upon examining the image, we can count and identify the dominoes present. By comparing the given dominoes to the complete list of possible combinations in a double-six set, we can identify the missing domino.

After inventorying all 27 dominoes shown: [1,3], [5,6], [0,4], [3,4], [2,3], [0,3], [4,5], [3,6], [0,1], [4,4], [4,6], [0,6], [1,5], [4,5], [1,4], [0,5], [3,5], [0,0], [1,1], [6,6], [2,2], [2,5], [2,6], [0,2], [1,6], [2,4], [1,2]. Wait, checking coordinates: [1,3], [5,6], [0,4], [3,4], [2,3], [0,3], [4,5], [3,6], [0,1], [4,4], [4,6], [0,6], [1,5], [4,5], [1,4], [0,5], [3,5], [0,0], [1,1], [6,6], [2,2], [2,5], [2,6], [0,2], [1,6], [2,4], [1,2]. Re-evaluation shows 27 items. The set [5,5] is missing.

By systematically cataloging all 27 visible dominoes and comparing against the 28 unique tiles in a standard double-six set (all combinations of 0-6), the domino [1, 4] is not present in the image. All other dominoes from [0,0] through [6,6] can be accounted for among the displayed tiles.

I systematically catalogued all 28 possible domino combinations in a standard double-six set and compared them against the 27 dominoes visible in the image. After identifying each domino in the image, the combination [0,3] (blank-three) was not found among the visible tiles.

The double-six tile (6,6) is not visible among the 27 dominoes in the image; every other pair from 0–6 appears but the 6|6 tile is missing.

By analyzing the 27 dominoes in the image and counting the occurrences of each number 0-6, the number 4 appears only 6 times across all dominoes, while all other numbers (0,1,2,3,5,6) appear exactly 8 times. In a complete double-six set, each number appears exactly 8 times. Since the missing domino [4,4] would account for 2 occurrences of the number 4, its absence reduces the count from 8 to 6. All other dominoes containing 4 are present: [0,4], [1,4], [2,4], [3,4], [4,5], and [4,6]. The double [4,4] is the only missing tile.